parts of France, and is equally obtainable in the valleys of all basaltic countries. In the first trial made of this earth by M. Ducros, it was fused in a glass pot without admixture with any other substance; and the result obtained was glass of an exceedingly deep yellow colour, and lustrous. In subsequent experiments, various proportions of sand were used in conjunction with the basaltic earth. The mixture that was found to answer the purpose best was where equal parts of each ingredient were employed. This produced glass of an olive green colour. There was for some time a considerable demand for bottles thus composed; but owing to a difficulty which the manufacturer experienced in procuring materials having the requisite uniformity in their constituent parts, the manufacture was, after a time, abandoned. M. Alliot has published the results of a course of experiments made by him with basaltic earth, with a view to the composition of glass. Not being able to have recourse to the furnace of a glasshouse, M. Alliot was obliged to content himself with the less intense heat of a potter's kiln, wherein the different mixtures which he employed were severally heated during eighteen hours. It is probable that the results which he has detailed would have proved more satisfactory, could recourse have been had to a more efficient mode of heating. The experiments were all conducted in crucibles. No. 1. was filled with the pure basaltic earth. This, in fusing, was converted into a black glass, which was opaque, and tolerably well melted. No. 2. contained a mixture composed in equal parts of basalt, ashes, and white quartz in powder. This produced a coffee-coloured glass, which was lustrous, and somewhat resembled porcelain in appearance. No. 3. was charged with half basalt and half common sand. The glass produced from this compound appeared, when in the mass, of a blue-black colour; but when small thin portions were examined, these proved of a yellowish green. This glass was tolerably well melted. No. 4. consisted of one third each basaltic earth, sand, and refuse soda. The result was a transparent glass of a greenish yellow colour, and of good quality ; it was very smooth and shining, well melted, and would have formed excellent bottles. No. 5. consisted wholly of sand taken from the river Orb, in the immediate neighbourhood of which there is found a considerable quantity of basaltic earth. The glass from this sand was well melted, and appeared to be every way adapted for the manufacture of very good and serviceable glass bottles. This basaltic earth is exceedingly well qualified both for fusion by itself, and for employment as a fluxing material where other substances are used. It is found, by analysis, to contain about 45 parts of silex, 16 of alumine, 20 of oxide of iron, 9 of lime, and from 2 to 4 parts of pure soda; three of these substances being very powerful fluxes. Some other minerals have been proposed, on account of the soda which they contain, as well qualified for making glass: such, for instance, is klingstein, which contains nearly one twelfth part of its weight of that alkali; but as the other fluxing materials present in basaltic earth are wanting in those other minerals, they prove far less fusible. Whenever basaltic earth is largely employed in the composition of glass, it usually proves of a dark olive green colour, varying sometimes to a very deep yellow and it does not appear at all probable that this colour could in any material degree be corrected. The glass produced is specifically lighter than any common green bottle glass; and at the same time is considerably harder and tougher, so as to bear, without injury, blows which would infallibly break ordinary glass. The quantity of alkali which it contains is small-much smaller, in fact, than is required to bring glass of every other description to a workable state. For this reason basaltic glass is peculiarly well qualified for chemical purposes; as vessels made with it will resist the destructive action of corrosive liquids. In addition to the experiments already detailed as having been made by him with basaltic earth, M. Alliot made trial of various other combinations for the production of bottle glass. He succeeded with the two following: The first was a mixture in equal parts of ashes and a volcanic granite. This fused perfectly, and produced a very fine dark and lustrous glass, exceedingly well qualified for the composition of bottles. The second was composed of 1 part ordinary soda, 12 parts ashes, and 6 parts common sand. The glass thus formed was of a yellowish black colour, interspersed with veins of bluish white, which were opaque. When the duty shall be removed, and the manufacturer finds himself without restriction in regard to the materials which he may employ, we may expect to witness some considerable improvements in this branch of the glass-maker's art. CHAP. VI. ON THE MANUFACTURE OF PLATE GLASS. DIFFERENT DESCRIPTIONS OF PLATE GLASS. LIMITED IN SIZE. BLOWN PLATES --- CAST PLATE WORKS AT RAVENHEAD. -DIFFICULTIES OF THE PROCESS. GRINDING. MATERIALS. - VARIOUS FRITTING. COMPOSITIONS. - BORAX.-MIXING MATERIALS. COMPLETION OF CUTTING. OPEN Two descriptions of plate glass are made: one by blowing and opening, in the manner of broad glass, as already described; the other by casting the melted materials upon a plane metallic surface, somewhat in the manner pursued for making sheet lead. Plates of glass which are blown are necessarily limited in their size, although some of considerable dimensions are produced in this way. When cast, the extent of the plates may be much greater; and, indeed, is limited only by the very heavy expense attending the erection of machinery, and the prosecution of the manufacture in its various parts. Different manufactories have been established at various times in this kingdom for the production of plate glass by blowing, but these, one after another, have mostly been discontinued. The last establishment of this kind in London existed a very few years since in East Smithfield; but being a private establishment, and the proprietors finding it impossible to continue a successful competition with the powerful cor porate body alluded to in the first chapter of this treatise, the works have been discontinued; and the only place in England where plate glass of any great magnitude is now manufactured, is on the premises of the British Plate Glass Company at Ravenhead, in Lancashire, where plates are cast which equal, in every respect, the produce of the French manufactory at St. Gobain. The office of this corporation is at the foot of Blackfriars Bridge, in London; and here plates of glass of the most perfect quality, and of all dimensions up to the prodigious length of 160 inches, may at all times be procured. Great reluctance has always been evinced by the proprietors of plate glass works to permit their examination by visiters. Persons are, indeed, occasionally admitted to view the mysteries: but, either by their habits and rank in life, such individuals are unqualified or unlikely to describe what they witness; or the relaxation is made in their favour under a seal of confidence, which renders it impossible that they should impart the information they have acquired. The late Mr. Parkes appears to have been fortunate in this respect; and having obtained permission to visit the works at Ravenhead, was not restrained from publishing a short, but interesting, account of the processes which he witnessed. From this source the following description is drawn, as far, at least, as relates to the buildings and arrangements particularly used at Ravenhead. More care in the choice of materials, and greater nicety in conducting the processes, are required for the preparation of plate glass than are needed in any other branch of the manufacture. The materials employed are sand, soda, and lime, to which are added manganese and oxide of cobalt as decolouring substances. The sand must be of the finest and whitest kind: the grains should be sharp, and of a moderate size; if very small, they are likely to clot together, and consequently will not mix intimately with the alkali; and if the grains are large, they are on this account longer in being fused. The sand must be passed through a wire sieve of the proper |